Re: [RFC PATCH 00/12] hw: Forbid DMA write accesses to MMIO regions

[Peter Maydell]

On Wed, 9 Sep 2020 at 10:12, Stefan Hajnoczi <stefanha@gmail.com> wrote:
>
> On Thu, Sep 03, 2020 at 01:08:19PM +0200, Philippe Mathieu-Daudé wrote:
> > The main patch is:
> > "exec/memattrs: Introduce MemTxAttrs::direct_access field".
> > This way we can restrict accesses to ROM/RAM by setting the
> > 'direct_access' field. Illegal accesses return MEMTX_BUS_ERROR.
>
> QEMU needs to simulate the behavior of real hardware. What is the
> behavior of real hardware?

It varies, depending on the hardware. The most common thing
is probably "happens to work by luck", which is OK for hardware
but doesn't help us much since our software implementation is
naturally more serialized than hardware is and since we don't
want to allow guests to make QEMU crash or misbehave.

thanks
-- PMM